In mononucleosis, which organ may be enlarged?

• A. Spleen
• B. Heart
• C. Liver
• D. Lungs

Answer: (A)

Mononucleosis often causes enlargement of the spleen because the Epstein-Barr virus drives lymphoid tissue proliferation, especially in the spleen’s white and red pulp. This splenomegaly reflects the immune system’s intense activation and cell turnover in response to the infection. The spleen becomes enlarged as part of this immune response, which is a classic finding in mono. While the liver can also become enlarged due to mild hepatitis, splenic enlargement is more characteristic and commonly emphasized in exam settings. The heart and lungs are not typically enlarged in straightforward mononucleosis. Knowing that splenomegaly is a typical feature helps you recognize mono and also highlights the clinical caution to avoid contact sports to reduce the risk of splenic rupture.